The crop of young male actors taking over our screens

Girls think Jake Gyllenhaal is gorgeous, boys reckon he's cool - and the 25-year-old is the leader of a pack of film stars with both box-office clout and art-house cred. But do any of these guys have what it takes to become the next George Clooney, asks David Thomson. Or will they take a wrong turn and go the way of Ben Affleck?

Jake Gyllenhaal handles himself like a pro at every turn. He has all the best deprecating jokes about an overnight sensation such as himself. He is a cool dude, which is the kind of young man young men today appreciate. He wonders with a dry voice and a dreamy gaze whether he'll be around long enough for people to learn how to spell his name. And he has a cynical version of how the fickle waves of fashion wash over someone like Jake: "First, it's 'Who is Jake Gyllenhaal?' Then it's 'Get me Jake', then it's 'Get me someone like Jake Gyllenhaal,' and finally it's 'Jake Gillenhall? Who's he?'"

In truth, that quick tour of the ups and downs might make a pretty good movie one day. It's also the kind of story that Jake has known most of his life. You see, he didn't exactly blow in from Wyoming on the Greyhound bus, as dumb and naïve and wistful as some midnight cowboy in the big city. Truth to tell, Jake is the son of Stephen Gyllenhaal, a film director of taste and accomplishment, even if he has never quite found himself in the big time that has gathered around his son's slim shoulders, and of Naomi Foner, an experienced screenwriter.

Jake was born not in the shadow of Brokeback Mountain, but in a place called Los Angeles. He grew up amid show business talk, with dinner plates and screenplays-in-progress fighting for room on the table. Jake's sister, Maggie, is also an actress (she was very striking in Secretary), and Jake graduated from Hollywood-Westlake High School, which is one of the inside schools in town, before he dropped out of Columbia after two years. I'm sure his parents were distressed at that, but I'm also sure that it was a household where every inhabitant - including the dog - knew that you don't expect the postman to knock twice. If you're being offered, you jump. That's how Jake Gyllenhaal, just 25, gets to be opening in three films in one season - Proof; Jarhead; and Brokeback Mountain. Look, Paul Newman taught the kid to drive, and Newman is a "go-for-it" guy who knew that James Dean's dying was the greatest opening he was ever going to get.

Gyllenhaal has made over 15 films already and he was beginning to be noticed in Donnie Darko, Lovely & Amazing and The Day After Tomorrow, but his breakthrough film, clearly, is Brokeback Mountain, in which he and Australian actor Heath Ledger defied a good deal of career advice and took on the roles of lovelorn ranch hands in Wyoming in the Sixties, guys hardly accustomed to use the word "love", let alone follow any homosexual urgings, but who find themselves passionate tent-mates in Ang Lee's picture from the Annie Proulx story.

Brokeback Mountain is not a hit in the style of King Kong or The Lion, the Witch and the Wardrobe, but it is drawing steady, sympathetic audiences on the art-house circuit; it has been banned already at one theatre in Utah; and it is gathering awards and nominations by the armful. It will be there on Academy Awards night, and I'd guess that the new host Jon Stewart is already calculating just what jokes he can make about the movie without offending. Jake Gyllenhaal is finding himself mentioned in the same breath as Montgomery Clift, who played a famously tough cowboy in Red River (1947), and who was gay, or bisexual, despite the resolute straight styling of his part in that film. Everyone today is tender enough to insist that Jake and Heath are straight arrows - it's just that they're good enough as actors to evoke the gay sensibility.

Meanwhile, Brokeback Mountain is serving as a focus to the intriguing crop of very young male actors who are taking over our screens. In a way, I think, that's a trend that began with Leonardo DiCaprio in Titanic. Nine years ago, that epic went from being a dreaded failure to a blockbuster in a matter of weeks - and as business experts pondered why, they reached the conclusion that teenage girls were going back over and over again to see Leonardo.

Notice that that passion has hardly lasted: his following diminished drastically with Gangs of New York and The Aviator. Neither of those films was as romantic as Titanic. But Leo had clearly aged - and being a teenager doesn't last very long. Still, the industry knows demographics now if it knows nothing else, and the trend was plain in TV, in the burgeoning world of arty fashion magazines and in movies, that "girls" got off on ogling pictures of young guys in very much the same way, for decades, men had made an industry out of wanting to look at women. And every four or five years, you've got a whole new generation of teenagers.

Heath Ledger is, in fact, the leading figure of this generation, and according to most judges its outstanding actor. Born in Perth, Western Australia, and about 20 months older that Gyllenhaal, Ledger gives a very subtle, yet savagely repressed performance in Brokeback Mountain, to such an extent that he is likely to be nominated for best actor, while Gyllenhaal is placed as a supporting actor. But Ledger's distress in the Ang Lee picture makes a terrific contrast with his sexual aplomb as Casanova, the film in which he shows how well suited he would be to play Errol Flynn, if ever anyone had that idea. Ledger really arrived on American screens in 2000 as the son in Mel Gibson's The Patriot. But he has moved fast: A Knight's Tale; Monster's Ball; The Four Feathers; Ned Kelly; The Brothers Grimm.

There are others. Hayden Christensen, born in Canada in 1981, is best known for his dark and smouldering Anakin in the two final episodes for Star Wars - Attack of the Clones and Revenge of the Sith - but he also played the disgraced American journalist Stephen Glass in Shattered Glass, and he has a string of new pictures in production. Michael Pitt is American, also born in 1981, and he had his breakthrough in the Bernardo Bertolucci film, The Dreamers, before doing Wonderland, Jailbait and Last Days. James Franco, aged 28, arrived as James Dean in a TV film; he's Tristan now in Tristan & Isolde and the lead in the Naval Academy drama Annapolis.

If you want an English candidate, there is Orlando Bloom, already 29, but very handsome, and a veteran of the three Lord of the Rings pictures, as well as Pirates of the Caribbean, one of the gang in Black Hawk Down, also in Ned Kelly, Paris in Troy and Balian in Kingdom of Heaven.

But as soon as one mentions Orlando Bloom, some problems arise in the absolute acceptance of this young gang. Troy and Kingdom of Heaven did no good to anyone's career - there are some films it's simply better to avoid. And though Bloom was there all along in Lord of the Rings, I think there's no doubt but that the trilogy did much more to boost the standing of Viggo Mortensen, who is all of 47! Indeed, Mortensen stands up for a quite different tradition: that of learning your craft gradually; improving over the years; and becoming a very good actor who can hold the screen with simplicity and confidence - as witness his work in A History of Violence.

Every one of the kids knows how tough it is to keep in place. They are all loners, without the support of studio contracts, and promoted largely by agencies that have a hundred other pretty boys on their books if one "star" goes out of fashion. This is the cruel condition that was once felt most forcibly by young actresses who were told to make an impact very young, be obliging and obedient and pray that their looks lasted until 30.

In other words, these young men are under terrible pressure to make the right choices - which means, be in the right films. The recent history of Hollywood is littered with movies that introduced a whole team of very young talent. Remember Francis Coppola's The Outsiders, from 1983, with this cast list - C Thomas Howell, Matt Dillon, Ralph Macchio, Patrick Swayze, Rob Lowe, Emilio Estevez, and Tom Cruise. It's not quite that everyone else has faded away, but 23 years ago I don't think Cruise would have been the automatic favourite to survive. That he did win out has something to do with his screen presence and his grin, but rather more with his instincts as a businessman and a career-maker.

Ben Affleck is still only 33. A few years ago, there were those who regarded him as an institution in the making. He and his pal Matt Damon had written Good Will Hunting, and Affleck was a heart-throb star - but one of his vehicles was the disastrous Pearl Harbor, and then came Gigli. Equally, Jude Law, still only 34, seemed poised to be a screen sensation after his Dickie Greenleaf in The Talented Mr Ripley. He was being offered a host of pictures, and he chose to do Cold Mountain, I Heart Huckabees, Sky Captain and the World of Tomorrow, the dreadful remake of Alfie, Closer (where he was the one callow person in the picture) and The Aviator (where he had just a cameo as Errol Flynn). He is young enough to make a comeback - he has All the King's Men finished, as well as Breaking and Entering - but his fortunes show how many other elements beyond an actor's control must fall in line if he is to do well.

Jake Gyllenhaal has shown a pleasing readiness to experiment: he did Kenneth Lonergan's This Is Our Youth on the London stage in 2002 (and won a prize for it). But he is shrewd enough in the ways of the business to know this: if early success inflates your pay level (from $1m a picture - a fabulous fortune for any young actor) to say $10m, or more, then you make yourself a liability, all the more vulnerable to the potential of some new kid, six months younger than you are, who is prepared to take the lead role in a new picture for so much less than your dignity will allow.

This does not mean that all the young men mentioned here are not desperate to act - to do good work. But they can easily lose control of their own careers if they trust too much to the agents and lawyers who "look after them". That's why every young star in this year has reason to look at George Clooney with immense respect.

As a matter of fact, Clooney will only be 45 this year. I know, he seems older sometimes, and in part that's because he winces a little at having been a pretty boy himself once in those years when he was a big attraction on ER and not much else. He had some very routine years, smirking his way through bad pictures, and flopping in anything more adventurous. But then something happened: moviegoers began to realise that they liked him, or trusted him. And then he branched out suddenly and made a very adventurous film, Confessions of a Dangerous Mind. It didn't do too well, but it was clear that Clooney knew how to direct.

Well, in 2005 he has had a better year than Heath Ledger - acting in and directing Good Night, and Good Luck, and acting in Syriana. Sure, he can say, with his grin, you have to make a few Ocean's 11 pictures to be able to do Good Night, and Good Luck. But that's how the real business has always worked. And George Clooney knows something that every kid is going to have to learn - that you might as well take full responsibility for what you make.

Because sooner or later, you're going to get the blame anyway. And Clooney knows this - he might have learnt it from his aunt, the singer Rosemary - that the longer you stay around the more the public thinks you're good company.

'Brokeback Mountain' is out now; 'Proof' is out on 10 February